The temperature outside must have been different each night, either that or your coop exists in an interdimesional rift where the laws of thermodynamics don't apply.
Just like a pot of warm water will come to a boil faster than a pot of cold water exposed to the same heat, cold water will freeze faster than warm water.
Warm water in many, but not all cases will in fact freeze faster then cold water this this has been proven for hundreds of years, and is called the Mpemba Effect... It doesn't contradict the laws of thermodynamics it contradicts the common understanding of thermodynamics, and shows our understanding of thermodynamics is not complete...
I think it is unlikely that one would witness the Mpemba phenomenon in two side by side chicken waterers.
Not unlikely at all, you can witness it pretty regularly in simple exerperiments...
You can even do the experiment in your own freezer using two bowls or cups of water started at different temps, and see it happen most of the time, it's common science experiment in schools and colleges to get the mind wondering...
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